docs: def group_by_month_per_hour(self):
          """Return a dictionary of this collection's values grouped by each month per hour.
  
          Key values are tuples of 2 integers:
          The first represents the month of the year between 1-12.
          The first represents the hour of the day between 0-24.
          (eg. (12, 23) for December at 11 PM)
          """
          data_by_month_per_hour = OrderedDict()
          for m in xrange(1, 13):
              for h in xrange(0, 24):
                  data_by_month_per_hour[(m, h)] = []
          for v, dt in zip(self.values, self.datetimes):
              data_by_month_per_hour[(dt.month, dt.hour)].append(v)
          return data_by_month_per_hour